In paper forms the specific sub-questions cannot be hidden from the user when they are not relevant to them - but in interactive forms this is relatively easy to do. Use progressive revealing as much as possible in your form design to shield your users from questions they do not need to see.

Make structure clear, and provide navigation to reinforce it. Your form will be divisible into sections so think about the broad groups of questions being asked. Whatever your groups of questions are, make sure they follow the right order and give the groups clear section names.